The present invention concerns a manufacturing method for electro-optical cells, in particular liquid crystal cells, or electrochemical photovoltaic cells, each cell including a transparent front substrate and a back substrate which may or may not be transparent onto which is formed a pattern of conductive elements forming electrodes and conductive paths connecting these electrodes to contact pads, the two substrates being bonded together by a sealing frame defining a sealed volume in which an active medium is confined. The present invention also concerns a cell obtained from this method.
"Electro-optical cell" is used to mean a display cell wherein the electro-optical features of the liquid crystals confined between the two substrates of said cell can be modified by electric control signals applied across the electrodes. Moreover, the electrochemical photovoltaic cells are cells capable of converting visible light into electricity by exploiting the photoelectric effect which appears in a semi-conductor substrate sensitised by a dye.
A batch manufacturing method for liquid crystal display cells of the type described hereinbefore will be examined with reference to FIGS. 1 to 3 annexed to the present Application, FIG. 1 being a partial schematic plane view of a batch of liquid crystal display cells during manufacturing, and FIGS. 2 and 3 being respectively a plane view and a cross-section along the line III--III of FIG. 2 of an individual display cell.
The above method consists in forming, conventionally by photolithography, on two large front and back substrates respectively 1 and 2 which are made of glass or a synthetic material and at least one of which is transparent, a pattern of conductive elements which are also transparent. These conductive elements form control electrodes 4 and 6. These electrodes 4 and 6 are situated at the location of pictures to be displayed and conductive paths connect them to contact pads 8 situated at the periphery of each cell 10. A network of material forming sealing frames 12 is then deposited on one of substrates 1, 2, said sealing frames each forming a sealed volume in which the liquid crystal will subsequently be confined. For this purpose, a filling aperture 14 is arranged in sealing frames 12 for each cell 10, then substrates 1, 2 are bonded to each other to form an assembly including several rows of open cells 10. This assembly is then divided into rectilinear strips 16 by glass scribing and breaking techniques, or by sawing along dividing lines 18 which form the longitudinal edges 20 of strips 16. These dividing lines 18 are rectilinear and parallel and are shown in dot and dash lines in FIG. 1. As filling apertures 14 are all situated along the same longitudinal edge 20 of strip 16, it is easy to fill cells 10 then to hermetically seal the filling apertures 14 thereof. Strips 16 are finally divided into individual rectangular cells 10 along straight lines perpendicular to the preceding lines. At this stage, if the contour of cells 10 has to have portions different from the rectangular shape, such portions are shaped by grinding. Any outer layers such as, for example, a polariser film 22, are applied subsequently, since otherwise there is a risk of the deterioration thereof by the cutting and grinding operations. These manufacturing steps which have to be effected individually on each cell 10 make manufacturing more complex and expensive than if they could be performed on a complete batch of cells 10.
Further, as shown in FIGS. 2 and 3, each cell 10 has a rectilinear edge 24 where back substrate 2 projects with respect to front substrate 1, in order to allow contact pads 8 to appear and thus to create a connection zone 26 which can be accessed to establish the electric connection between electrodes 4, 6 of cell 10 and an electric control circuit (not shown) capable of modifying the electro-optical features of the liquid crystal. As is clear from FIG. 1, connection zones 26 of cells 10 are all aligned along one of longitudinal edges 20 of strips 16 and are opposite to filling apertures 14 of cells 10.
Rectilinear edge 24 of cells 10 is conventionally marked by scribing by means of a diamond tool, so that lines of least mechanical resistance 28, which are rectilinear and parallel to dividing lines 18, are generated at the surface of front substrate 1. After cutting out a strip 16, the glass can be broken manually along line 28, by slight bending transversely to said line 16, thus allowing connection pads 8 of cells 10 to appear.
The above glass scribing and breaking operation is relatively simple to implement. Cells 10 thereby obtained have, however, the significant drawback of having only one connection zone 26, which limits the number of available connection pads 8, and thus the number of pictures which it is possible to display by means of such a cell 10. In order to overcome this difficulty, a known solution consists in multiplexing electrodes 4, 6 of cells 10, which means that a same electrode can control the display of at least two different pictures. It has however been observed that the nigher the multiplexing rate of electrodes 4, 6, the less satisfactory the resulting optical display quality.
There therefore existed a need in the state of the art for display cells having two connection zones 26 instead of a single such zone. One possible solution to this problem would have been to envisage arranged connection zones 26 not opposite filling apertures 14, i.e. longitudinally to strips 16, but transversely to said strips 16. A major prejudice has however always opposed the implementation of this solution.
It is known that glass scribing by means of a diamond tool generates at the surface of the glass a network of superficial mechanical stress which contribute to breakage of the glass at the place where it was scribed. It was nonetheless commonly admitted to date that the glass had to be broken shortly after being scribed. It was thought that if this was not the case, the network of stress generated by scribing the glass would tend to relax so that the glass would break less cleanly and would have irregularities which are unacceptable within the field of display cell manufacture. It is for this reason that connection zones 26 of cells 10 have until now always been aligned along one of longitudinal edges 20 of strips 16, so that the glass of front substrate 1 could be broken shortly after having been scribed, i.e. immediately after cutting a strip 16. However, in the hypothesis in which connection zones 26 are arranged transversely to strip 16, the bending of said strip 16 would not allow the glass between two adjacent cells 10 to be broken. This operation would thus have to be performed after application of polariser films 22, a long and difficult step, and dividing cells 10 individually. It was thus thought that the period of time between the moment when the glass is scribed and the moment when the latter is broken was too long and make this operation impossible because of the phenomenon of stress relaxation described hereinbefore. This is why those skilled in the art has always rejected this solution to date.